It is well known to treat metal surfaces such as iron and steel with some form of corrosion inhibiting treatment or coating. Corrosion inhibiting coatings are well known in the art and generally contain metal particles in particular zinc and/or aluminium particles as active ingredients together with some form of binder.
GB 1380748 describes a coating composition particularly, but not exclusively, for a zinc filled coating composition which when applied to a metal surface will provide galvanic protection to the metal. The composition comprises trialkoxysilanes which have been cohydrolysed and cocondensed with a hydrolysable titanium ester. The Silane is selected from RSi(OR′)3 and RSi(OR″OR′″)3 where R and R′ are monovalent aliphatic or aromatic hydrocarbon radicals having up to 10 carbon atoms, R″ is a divalent hydrocarbon radical having from 2 to 6 carbon atoms and R′″ are monovalent aliphatic or aromatic hydrocarbon radicals having up to 10 carbon atoms or hydrogen.
GB 1499556 relates to a process for hydrolyzing ethyl silicate to form a gellable liquid hydrolysate which is used for mixing with powders such as powdered zinc for use in an anti-corrosion paint. The ethyl silicate is acid hydrolysed and the solvent for the hydrolysis is acetone or an alcohol
EP0808883 discloses a water-reducible coating composition for corrosion protection comprising particulate metal such as aluminium or zinc and a water reducible organofunctional silane. Epoxy silanes, particularly beta-(3,4-epoxycyclohexyl)ethyltrimethoxysilane and/or gamma glycidoxypropyltrimethoxysilane were preferred. Other constituents included a high boiling point organic liquid, a water soluble cellulose based thickener and a wetting agent.
U.S. Pat. Nos. 5,393,611 and 5,324,545 both relate to a dip-coating method for protecting chromatised or passivated zinc coatings on steel or the like using a composition of a titanic acid ester and a “so-called” organofunctional polysiloxane, preferably having between 2 and 10 siloxane repeating units and epoxy end groups. There is no clear definition of the meaning of the term organofunctional polysiloxane in either of these documents but it would seem to mean a polymer with a siloxane backbone having at least one Si—R bond where R is an unsaturated or functionally substituted hydrocarbon radical. Confusingly however the examples in U.S. Pat. Nos. 5,393,611 and 5,324,545 both teach that rather than an organofunctional polysiloxane being used the preferred silicon containing compound is an epoxy silane, namely gamma glycidoxypropyltrimethoxysilane.
The present inventors have found an increasing demand from industry for coatings for metal surfaces which can provide a high level of corrosion protection, cathodic protection, and “for-life” dry lubrication (i.e. the metal surface needs coating only once during its working life) with defined and constant coefficient of friction, whilst being Chromium VI-free and providing an attractive appearance to articles coated with the coating. Commercially available coatings are unable to satisfy all of these demands.